Touch sensitive electronic switch

ABSTRACT

A touch sensitive electronic switch which has no moving parts and is actuated by the skin resistance of an operator causing a lowering of D.C. resistance across the switch is disclosed. The electronic switch shown includes two electrodes laterally spaced and insulated from each other. The top surfaces of the electrodes are exposed to the finger of the operator upon the top surface of an insulator mounting the electrodes in a manner that the operator&#39;&#39;s finger first touches an outer electrode and then an inner electrode to allow a direct current path to be set up laterally between the outer electrode and the inner electrode to thereby provide a lowering of the D.C. resistance across the switch. The relationship of the top surface of the outer electrode and the top surface of the inner electrode insures that the finger of the operator first touches the outer electrode before contact is made between the finger and the inner electrode to thereby allow the harmless grounding of the usual voltage in the operator&#39;&#39;s body.

United States Patent [191 Larson 1 3,715,540 51 Feb. 6, 1973 [54] TOUCHSENSITIVE ELECTRONIC SWITCH Willis A. Larson, Wayzata, Minn.

52 U.S.Cl. ..200/159 R,200/D1G.2 51 Int. (:1. ..H0lh s s 0 0 DIG. 2;317/DIG. 2, DIG. 1; 307/116 [56] References Cited UNITED STATES PATENTS2,186,825 1/1940 Dome.. ..250/20 2,576,929 12/1951 Ercolino ..200/l59 AX 2,659,533 11/1953 Quinby et al. ..200/DIG. 1 3,320,438 5/1967 Myers..200/DIG. 1

OTHER PUBLICATIONS Johnson, IBM Technical Disclosure Bulletin, April,

1971, Vol. 13, No. 11, p. 3551 (Pushbutton switch with no moving parts)Primary Examiner-l-Ierman J. I-Iohauser Assistant Examiner-William J.Smith AttorneyJack W. Wicks et a1.

[57] ABSTRACT A touch sensitive electronic switch which has no movingparts and is actuated by the skin resistance of an operator causing alowering of DC. resistance across the switch is disclosed. Theelectronic switch shown includes two electrodes laterally spaced andinsulated from each other. The top surfaces of the electrodes areexposed to the finger of the operator upon the top surface of aninsulator mounting the electrodes in a manner that the operators fingerfirst touches an outer electrode and then an inner electrode to allow adirect current path to be set up laterally between the outer electrodeand the inner electrode to thereby provide a lowering of the DC.resistance across the switch. The relationship of the top surface of theouter electrode and the top surface of the inner electrode insures thatthe finger of the operator first touches the outer electrode beforecontact is made between the finger and the inner electrode to therebyallow the harmless grounding of the usual voltage in the operators body.

2 Claims, 2 Drawing Figures TOUCH SENSITIVE ELECTRONIC SWITCH CROSSREFERENCES Warner, Jr.,"Ser. No. 199227, entitled Composite D.C.Amplifier For Use With A Touch Sensitive Electronic Switch; Willis A.Larson, Ser. No. 199195, entitled Touch Sensitive Electronic Switch; andWillis A. Larson and Arthur Kimmell, Ser. No. 199384, entitled TouchSensitive Electronic Switch.

BACKGROUND This invention relates generally to electronic switching, andmore specifically to a touch sensitive electronic switch which has nomoving parts and is actuated by the skin resistance of an operatorlowering the D.C. resistance across the switch to provide a D.C.

input signal to a D.C. amplifier.

In the above referred to original application by Willis .A. Larson, theadvantage in a touch sensitive electronic switch of the operator sfinger first making contact with an electrode arranged to be connectedto the voltage supply terminal of a D.C..amplifier before contact ismade with an electrode arranged to be connected to the input of a D.C.amplifier was disclosed. As was stated, this arrangement allows goodcontact of the operators finger with the supply connected electrodebefore contact is made with the input connected electrode and therebyallows the harmless grounding of the usual alternating voltage inducedfrom an external source into the operators body.

Variance of the touchthreshold of such a switch was further disclosed byvarying the depth of the input connected electrode with'respect to thesupply connected electrode. It was indicated that the deeper the inputconnectedelectrode was placed with respect to the supply connectedelectrode, the heavier the touch required to force the fingertip intocontact-with both touch threshold required to reliably actuate theswitch.

Also, because of the relationship of the present invention, a touchsensitive electronic switch may now be designed with more specificitythan heretobefore possi ble. Once the minimum depth to provide reliablegrounding of the voltage within an operators body is known, the actualdepth for which the' switch is SUMMARY In summary, a preferredembodiment of the present invention includes a first electrode immovablyarranged within a housing and a second electrode also immovably arrangedwithin the housing. The second electrode is further arranged around andabout and laterally spaced and insulated from the first electrode. Thefirst and second electrodes are exposed to the finger of an operatorupon the top surface of the insulating media of the housing in a mannerthat an opera tors finger touches the second electrode and then thefirst electrode to allow a direct current path to be set up laterallybetween the second and first electrode. The direct current path providesa lowering of the D.C. resistance across the electronic switch toprovide an input signal to a D.C. amplifier which can be used with theelectronic switch. The vertical distance between the top surface of thesecond electrode and the top surface of the first electrode, which isalso termed the height differential between the electrodes, and thelateral distance or spacing between the electrodes, and

the dimensions of an operators finger have been found 7 to beinterrelated in a fashion which allows a switch design minimizing :thetouch sensitivity'or threshold of the switch and yet insuring a heightdifferential between the electrodes which will allow grounding of thevoltage in an operators body by the second electrode before a directcurrent path is set up between the second electrode and the firstelectrode.

7 It is thus an object of the present invention to provide a touchsensitive electronic switch which may be designed with more specificitythan heretofore possible.

It is a further object of the present invention, to provide such anelectronic switch wherein the spacing and height differential betweenelectrodes can be more precisely specified to insure a grounding ofvoltage in an operators body and yet provide a minimum or near minimumtouch sensitivity, if desired.

It is a further object of the present invention to provide such anelectronic switch wherein the. height difdesigned maybe varied from theminimum depth to thus vary the touch threshold of the switch.

ferential between electrodes may be varied to .thereby vary the touchthreshold or touch sensitivity, if desired.

These and further objects and advantages of the present invention willbecome clearer in light of the fol lowing detailed description of anillustrative embodiment of this invention described in-connection withthe drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 showsv a prospective view of theelectronic switchof the present invention showing the disposition of theelectrodes and housing especially adapted for printed circuit board use;and

FIG. 2 is an enlarged cross section taken along the lines 2-2of thehousing illustrated in FIG. 1.

DESCRIPTION As disclosed in the above referred to original applicationby Willis A. Larson, in the figures, a switch 30 is shown as including ahousing 32, which may be made of any suitable durableinsulatingmaterial, and a switch face 39. Switch 30 is shown as it wouldbe utilized in a I printed wiring board. A dust seal of foam rubber orthe like is placed between a flange 152 of housing 32 and a panel 153through which the housing extends for manual access.

As best shown in FIG. 1, the electronic switch electrodes comprise aninput, first, or center electrode 50, and a supply, second or annularelectrode 42 concentrically disposed to center electrode 50, butextending longitudinally upward beyond the uppermost limit of the centerelectrode 50. The center electrode 50 and the annular electrode 42 areseparated and held in their respective positions by an insulator ring154.

It will be observed in FIG. 2 that the insulator ring 154 takes the formof a hollow cylinder to provide a chamber 158 into which the electroniccomponents of a high gain D.C. amplifier may be placed, as is discussedin the original application. A pair of hollow conductors 160 areembedded in the bottom portion of housing 32 to provide communicationwith the chamberl58. These hollow conductors permit a pair of leads tobe brought from chamber 158 to the lower surface of a printed wiringboard 162 where they may be soldered into place in the usual manner. Thesolder will also adhere to the hollow conductors 160 to provide a thesmallest finger expected to operate the electronic 50 of the electronicswitch of the present invention may now be explained. As'is shown in thefigures, center electrode 50 is immovably arranged with insulating ring154, with a top surface of the electrode 50 exposed to the finger of anoperator, a portion 144 of which is shown in FIG. 2, upon the topsurface of the insulating ring 154. Annular electrode 42 is alsoimmovably arranged with the insulating material of housing 32 and theinsulating ring 154, and with electrode 50, and is arranged laterallyaround and about, spaced, and insulated from electrode 50 in a manner toexpose the top surface of the annular electrode 42 to the finger of anoperator upon the top surface of the surrounding insulating material.THe level of the top surface of annular electrode 42 is further arrangedabove the level of the top surface of center electrode 50 in a mannerthat the fingerof the operator touches annular electrode 42 beforecontact is made between the finger and center'electrode 50 to therebyallow good contact of the operator's finger with annular electrode 42before contact is made with center electrode and thereby allow theharmless grounding of the usual voltage induced from external sourcesinto the operators body. This arrangement of electrodes also allows adirect current path to be set up laterally between center electrode 50and annular electrode 42 as soon as the finger of the operator touchescenter electrode 50.

The specific arrangement and relationship of the present inventionbetween the heretofore set out parts of electronic switch 30 may now beexplained. It has been found that the relationship between the level ofthe top surface of center electrode 50 and the level of the top surfaceof annular electrode 42 and the lateral spacing between center electrode50 and annular electrode 42 is such that P is at least equal to R minusthe square root of the quantity (R Y where P represents the heightdifferential between the level of the top surface of center electrode 50and the level of the top surface of annular electrode 42, Y representsswitch of the present invention.

That is, the mathematical expression may be set out as follows:

The height differential is directly related to the touch threshold ortouch sensitivity of the electronic switch 30 of the present invention.That is, with a height dif ferential in excess of P as established bythe above expression, the bottom of the finger must be further extendedfrom the point at which the inside edge 164 of electrode 42 is firsttouched by the finger to the point at which the bottom-most portion ofthe finger first touches the center electrode 50, the position of fingerportion 144 shown in FIG. 2.

Further, as shown, Y is the lateral spacing between the electrodes astaken between the center line of the center electrode 50 and the insideedge 164 of the annular electrode 42. It has been found, however, thatif the width of the center electrode 50 is below a value approximately10,000ths of an inch, Y may be taken as the spacing between the centerelectrode 50 and the annular electrode 42, that is between the outeredge of the center electrode 50 and the inner edge of the annularelectrode 42. Configurations of switch 30 where the center electrode maybe less than ten thousandths of an inch are set out in the abovereferred-to application for patent filed of even date herewith by WillisA. Larson, entitled Touch Sensitive Electronic Switch.

The curvature of a finger can be most simply expressed as an approximateradius. That is, most fingers range from between A; of an inch radius to4/8ths of an inch radius. However, if it is desired to obtain a moreexact relationship, the curvature of the finger may be expressed as amathematical expression of this expression substituted for R. Ingeneral, it has been found sufficient to determine the approximateradius of the smallest finger expected to operate the electronic switch30 of the present invention and use that particular number for R in theexpression, as a worst case condition.

OPERATION Generally, in operating the touch electronic switch 30 shownin the figures, the finger of an operator is placed upon the switch face39, for example as shown by the finger portion 144 shown in FIG. 2. Theelectrical skin resistance of the operator causes a direct current pathto be set up between the center electrode 50 and the annular electrode42 to thus cause a small current to flow between these electrodes. Thecurrent flowing is generally in the nanoamperes range (30-300nanoamperes) with normal skin resistances and a supply voltage ofapproximately 5 volts. This current may then be amplified by a DC.amplifier to a point where an output current is provided, thusapproximating an electronic switch in the closed or ON condition to anelectrical load. When the operators finger 144 is removed from switch30, the characteristics of the switch prevent any current flow acrossthe switch thus providing no input current which can be amplified, thusapproximating an electronic switch in an open or OFF condition to anelectrical load.

It is to be noted that actuation of the switch 30 of the presentinvention is made without movingparts, aside from movement of theoperators finger. That is, each of the supply electrode 42 and inputelectrode 50 is laterally immovably attached to housing 32. Laterallyimmovably attached for the purposes of this invention is defined aswhere the input and supply electrodes are fixed with respect to eachother in a manner to prevent the input electrode from coming into directelectrical contact with the supply electrode. Either electrode may bemade vertically movable, as by using a soft or spongy material orsprings to give the effect or feeling of vertical movement to anoperators finger. Other means for effecting this illusion of verticalmovement upon actuation will be envisioned by those skilled in the art.

The relationship of the present invention allows a switch designminimizing the touch sensitivity or threshold of the switch and yetinsuring a height differential between the electrodes which will allowgrounding of the alternating voltage in an operators body by the annularelectrode 42 before a direct current path is set up between the annularelectrode 42 and the center electrode 50. As explained in the originalapplication, if it were possible to touch the center electrode 50without first touching the annular electrode 42, the usual alternatingvoltage induced into the operators body from external sources wouldcause the switching system to turn ON and OFF at the alternatingfrequency, typically 60Hz. That is, in the normal case where centerelectrode 50 is arranged to be connected to the input of a D.C.amplifier, the alternating voltage existing in the operators body canalternately turn the D.C. amplifier ON and OFF and thus cause analternating switch output, i.e. where the output turns ON and OFF at thealternating frequency. Where a D.C. switch output is desired uponcontact of the operators finger with switch face 39, this is adetrimental result. Since annular electrode 42 is arranged to beconnected to a voltage supply terminal of the D.C. amplifier, insuringthat the operators finger first contacts annular electrode 42 insuresthat the alternating voltage within the operators body will be conductedto the. switch through the supply terminal. Also, static electricitywithin an operators body can exist within a range of 1,000 to 10,000volts, and any rapid discharge of this static electricity through inputelectrode 50 and to the input to a D.C. amplifier can damage the inputstage. It is thus also best for the purposes of discharging the staticelectricity that the finger of an operator first discharge the staticelectricity through the annular supply electrode 42. It is furtherdesirable if the annular supply electrode 42 has sharp corners to thusprovide the best discharge path. Thus, when the operators finger makescontact with the center electrode 50, the voltage has been eliminatedand what remains is a D.C. bridging of electrodes 42 and 50 to provide alowering of D.C. resistance across switch face 39 thus providing anactuation of the switch andits associated D.C. amplifier. Theelimination of the voltage within the operators body is particularlyimportant since the current input to the D.C. amplifier can be as low as30 nanoamperes, which can be easily overshadowed by the current causedby the alternating voltage within an operators body or the amperagerange current which can be caused by a rapid discharge of the staticelectricity within an operators body.

By use of the relationship of the present invention between P, Y, and R,the minimum offset between the center electrode 50 and the annularelectrode 42 may be determined. That is, the minimum spacing can bedetermined at which a finger of a given radius can contact an electrode50which is set below the level of an electrode 42 arranged around andabout electrode 50.

It has further been found that in order to reliably insure that thefinger of an operator will in fact contact the supply electrode beforecontact is made with the input electrode to allow the harmless groundingor referencing of voltage in the operators body, the height differentialfor which the switch 30 of the present invention should be designedexceeds the minimum. That is, the practical measure of P should exceedthe quantity R minus the square root of the quantity (R Y) to allow formanufacturing tolerances, differing finger characteristics as far as theability of the skin to compress, various finger placements upon switch30, and to allow for a variance of the touch threshold. That is, oncethe relationship of parameters of the present invention is known, theheight differential between the electrodes may be set beyond the minimumnecessary to insure grounding or referencing of the voltage within anoperators body and to such an increased level as desired to establish aparticular touch threshold for the switch. Applications may be desiredwhere the touch threshold is extremely light for all ranges of fingers,such as a general purpose application. Other applications may be desiredwhere the touch threshold is exceedingly heavy, such as in a switchwhich may be used on an armament where an undesired actuation wouldcause an extremely dangerous condition. Further applications may bedesired with intermediate touch thresholds.

Thus, since the invention disclosed herein may be embodied in otherspecific forms without departing from the spirit or generalcharacteristics thereof, some of which forms have been indicated, theembodiment described herein is to be considered in all respectsillustrative and not restrictive. The scope of the invention isindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is: I

1. Electronic switch apparatus operable by the lateral bridging of theswitch electrodes by the skin resistance of an operator, comprising incombination: insulating media having a top surface; first electrodemeans laterally immovably arranged with the insulating media with thetop surface of the first electrode extending from and exposed to thefinger of an operator upon the top surface of the insulating media;second electrode means laterally immovably arranged with the insulatingmedia and the first electrode laterally around and about, spaced andinsulated from the first electrode with the top surface of the secondelectrode extending from and exposed to the finger of an operator uponthe top surface of the insulating media laterally from the firstelectrode and with the relationship between the level of a top surfaceof the first electrode and the level of the top surface of the secondelectrode and the lateral spacing between the first electrode and thesecond electrode such that P is at least equal to R minus the squareroot of the quantity (R Y where P the first electrode and thereby allowthe harmless grounding of the voltage in an operator's body and allow adirect current path to be set up laterally between the first electrodeand the second electrode as soon as the finger of the operator touchesthe first electrode.

2. The electronic switch apparatus of claim 1, wherein P is greater thanthe quantity R minus the square root of the quantity (R Y) to allow forvariance of the touch threshold of the switch.

1. Electronic switch apparatus operable by the lateral bridging of theswitch electrodes by the skin resistance of an operator, comprising incombination: insulating media having a top surface; first electrodemeans laterally immovably arranged with the insulating media with thetop surface of the first electrode extending from and exposed to thefinger of an operator upon the top surface of the insulating media;second electrode means laterally immovably arranged with the insulatingmedia and the first electrode laterally around and about, spaced andinsulated from the first electrode with the top surface of the secondelectrode extending from and exposed to the finger of an operator uponthe top surface of the insulating media laterally from the firstelectrode and with the relationship between the level of a top surfaceof the first electrode and the level of the top surface of the secondelectrode and the lateral spacing between the first electrode and thesecond electrode such that P is at least equal to R minus the squareroot of the quantity (R2 - Y2) where P represents the heightdifferential between the level of the top surface of the first electrodeand the level of the top surface of the second electrode, Y representsthe lateral spacing between the first electrode and the secondelectrode, and R represents the curvature of the smallest fingerexpected to operate the electrical switch, the relationship insuringthat the finger of an operator touches the second electrode beforecontact is made between the finger and the first electrode to therebyallow good contact of the operator''s finger with the second electrodebefore contact is made with the first electrode and thereby allow theharmless grounding of the voltage in an operator''s body and allow adirect current path to be set up laterally between the first electrodeand the second electrode as soon as the finger of the operator touchesthe first electrode.
 1. Electronic switch apparatus operable by thelateral bridging of the switch electrodes by the skin resistance of anoperator, comprising in combination: insulating media having a topsurface; first electrode means laterally immovably arranged with theinsulating media with the top surface of the first electrode extendingfrom and exposed to the finger of an operator upon the top surface ofthe insulating media; second electrode means laterally immovablyarranged with the insulating media and the first electrode laterallyaround and about, spaced and insulated from the first electrode with thetop surface of the second electrode extending from and exposed to thefinger of an operator upon the top surface of the insulating medialaterally from the first electrode and with the relationship between thelevel of a top surface of the first electrode and the level of the topsurface of the second electrode and the lateral spacing between thefirst electrode and the second electrode such that P is at least equalto R minus the square root of the quantity (R2 - Y2) where P representsthe height differential between the level of the top surface of thefirst electrode and the level of the top surface of the secondelectrode, Y represents the lateral spacing between the first electrodeand the second electrode, and R represents the curvature of the smallestfinger expected to operate the electrical switch, the relationshipinsuring that the finger of an operator touches the second electrodebefore contact is made between the finger and the first electrode tothereby allow good contact of the operator''s finger with the secondelectrode before contact is made with the first electrode and therebyallow the harmless grounding of the voltage in an operator''s body andallow a direct current path to be set up laterally between the firstelectrode and the second electrode as soon as the finger of the operatortouches the first electrode.